High molecular weight linear polyesters and copolyesters of glycols and terephthalic or isophthalic acid have been available for a number of years. These are described inter alia in Whinfield et al, U.S. Pat. No. 2,465,319 and in Pengilly, U.S. Pat. No. 3,047,539. These patents disclose that the polyesters are particularly advantageous as film and fiber formers.
Such polyesters have not been widely accepted for use as molding resins, however, until only fairly recently, because of their relative brittleness in thick sections when crystallized from the melt. This problem was overcome by varying the crystal texture, e.g. by using two-step molding cycles or including nucleating agents, and by molecular weight control. This permitted the marketing of injection moldable poly(ethylene terephthalates) which typically, in comparison with other thermoplastics, offered a high degree of surface hardness and abrasion resistance, and lower surface friction.
Simultaneously with the development of injection molding grades of polyester resins, fiber glass reinforced compositions were also provided. See Furukawa et al, U.S. Pat. No. 3,368,995 and Zimmerman et al, U.S. Pat. No. 3,814,725. These injection moldable compositions provided all of the advantages of unfilled polyesters and, also, because of the glass reinforcement had higher rigidity, yield strength, modulus and impact strength.
Pristine, or sizing free, glass fibers have been disclosed as reinforcing agents in Abeleen et al, U.S. Pat. No. 4,539,350 and Abeleen et al, U.S. Pat. No. 4,568,712. These two patents teach the addition of a polysiloxane compound to improve the ductility of the polyester resins.
Conventional starch based sizings have been disclosed in the prior art. Abolins, in U.S. Pat. No. 3,671,487 teaches the use of lightly sized or unsized glass fibers in preparing flame and drip retardant glass reinforced polyester resins. Wambach, in U.S. Pat. No. 4,113,692 employs conventional sized glass fibers and polycarbonate resins to increase resistance to warpage in poly(1,4-butylene terephthalate) and poly(ethylene terephthalate) resin blends. Similarly, warp resistant polyesters with glass filaments in combination with talc or mica fillers are disclosed in United Kingdom Pat. Nos. 1,592,205 and 1,592,668, but sizings are conventional and are either optional or lightly employed.
Non-starch aqueous sizings for treating glass fibers are disclosed in Temple et al, U.S. Pat. No. 4,394,475. The patentee therein teaches a sizing composition comprising a non-starch film forming polymer, a polyethylene containing polymer and a wax which improves the slip/flow characteristics of the glass fibers.
Epoxy coated glass fibers to reinforce polymer materials are disclosed in Watson, U.S. Pat. No. 4,487,797 and Das et al, U.S. Pat. No. 4,745,028. Watson teaches an aqueous chemical composition comprising a water dispersible, emulsifiable or soluble epoxy novolac film forming polymer in combination with a glass fiber coupling agent and a poly(oxyalkylene-oxyethylene)polyol copolymer as the sizing agent. Das et al, teach a sizing composition which comprises an aqueous epoxy polyurethane with blocked isocyanate crosslinking groups and at least one or more organo coupling agents. Ogawa et al, U.S. Pat. No. 4,276,208 describe polyester resin compositions having glass fibers surface coated with an epoxy compound having at least two epoxy groups in the molecules such as bisphenol-A type epoxy compound, bisphenol-F type epoxy compound and novolac type epoxy compound, in combination with a salt of a montan wax.
None of the above patents contemplate the use of a sizing agent comprising a di- or tri- functional cyanurate or isocyanurate to impart reinforcement on polyester resins. Unexpectedly it has now been found that thermoplastic resin compositions comprising a polyester resin and a glass fiber reinforcing agent treated with a sizing agent comprising a di- or tri-functional cyanurate or isocyanurate surprisingly exhibit a marked increase in physical strength characteristics such as tensile strength, flexural strength and unnotched and notched impact strength over polyester resins treated with the prior art reinforcing agents.
Also to be mentioned is Japanese Pat. No. 73/25066 (See Chemical Abstracts 80,1974-134460k) which discloses increasing the bonding strength between poly(vinyl chloride) and silane-treated glass fiber reinforcement by treating a glass fiber roving with 3-aminopropyltriethoxysilane and triglycidyl isocyanurate. No mention, however, is made of using such treated glass fibers with polyesters or the surprising improvements in physical strength characteristics polyesters exhibit when treated with glass fibers sized with the disclosed compound.
Di- and tri- functional isocyanurates are disclosed in combination with glass reinforced polyester compositions in Japanese Pat. No. 53/144954 (Chem. Abs. 90(18):138661f); Japanese Pat. No. 53/144955 (Chem. Abs. 90(24):187948p); Japanese Pat. No. 53/143649 (Chem. Abs. 90(18):138625d); Japanese Pat. No. 53/106750 (Chem. Abs. 90(6):39670b); and Japanese Pat. No. 53/106749 (Chem. Abs. 90(4):24261v). It is believed, however, that the di- and tri-functional isocyanurates are employed as crosslinking agents in the polyester resins and not as novel sizing agents for the glass fiber reinforcing agents which provide unexpected marked increases in the physical strength of the polyester resins surprisingly found herein.